Conventional mechanically-driven water pumps typically have a structure that includes a mechanical seal and a lip seal, and supports a rotating shaft on a ball bearing (see Patent Documents 1 and 2, for example).
In hybrid vehicles and electric vehicles, electric pumps that allow more accurate thermal management than mechanical belt-driven ones have been used in recent years against a backdrop of fuel savings. It is expected that electric pumps will become used in water pumps for general automobiles in the future.
There are two types of electric pumps, a seal-less structure called a canned type (see Patent Document 3, for example), and a seal mechanism-equipped type like mechanical belt-driven water pumps (see Patent Documents 4 and 5, for example).
Since the canned type is seal-less, there is no fear of water leaks. On the other hand, the canned type has a structure in which a stator and a rotor are separated by a partition wall (a can 26 in Patent Document 3), and thus has problems of a great power loss and a very high cost when using a permanent magnet.
By contrast, the seal mechanism-equipped type has a risk of water leaks since it uses a seal mechanism as shown in FIG. 3. However, the seal mechanism-equipped type has a small power loss between an induction coil (on the stator side) and a magnet (on the rotor side), can use a small-sized magnet, is lower in cost than the canned type, and may become widely used in the future.